Abstract
An integrated survey program involving geological, hydrogeological and geophysical techniques has been employed to characterize the aquifer geometry, recharge and circulation dynamics of thermal springs within a shallow aquifer system in Ethiopia. The selected springs for the case study are Sodere and Gergedi, which are situated within the tectonically active Main Ethiopian Rift (MER). Geologically, the studied springs are located on Plio-Quaternary volcanic rocks. The geophysical results indicate the presence of subsurface weak zones represented by extensional tectonics and weathering zones which are responsible for thermal water circulation and facilitate recharge from the adjacent surface-water bodies. The structures inferred by the resistivity survey, both sounding and electrical tomography, present contrasts in rock resistivity response. The anomalous zones in the magnetic data are in good agreement with the zones that are revealed by geological mapping and surface manifestation of the thermal water discharge zones. The shallow aquifer of the central MER is under the influence of thermal water, which increases the groundwater temperature and mineral content.
Résumé
Un programme d’investigation intégrée comprenant géologie, hydrogéologie et géophysique a été mis en œuvre afin de caractériser la géométrie de l’aquifère, la recharge et les circulations thermales au sein d’un aquifère de surface en Ethiopie. Les sources retenues pour ce cas d’étude sont les sources de Sodere et de Gergedi, qui sont localisées au sein du rift éthiopien tectoniquement actif (RE). Du point de vue géologique, les sources étudiées émergent au niveau des formations volcaniques du Plio-Quaternaire. Les résultats géophysiques indiquent la présence de zones souterraines « faibles » correspondant aux zones d’extension tectonique et d’altération, responsables de la circulation des eaux thermales et facilitant la recharge des eaux de surface. Les structures mises en évidence à partir des sondages et des tomographies électriques, sont associées à des réponses contrastées en termes de résistivité. Les zones d’anomalies magnétiques sont cohérentes avec les zones identifiées lors de la cartographie géologique et par les zones de décharge des eaux thermales. L’aquifère de surface de la partie centrale du RE est influencé par les circulations des eaux thermales, ayant pour conséquence une augmentation de la température des eaux souterraines et de la minéralisation.
Resumen
Se empleó un programa integrado de relevamiento que involucra técnicas geológicas, hidrogeológicas y geofísicas para caracterizar la geometría del acuífero, la recarga y la dinámica de circulación de los manantiales termales dentro de un sistema acuífero somero en Etiopía. Los manantiales seleccionados para el caso de estudio son Sodere y Gergedi, los cuales están situados dentro del Rift Principal Etíope (MER) tectónicamente activo. Geológicamente los manantiales están localizados en rocas volcánicas Plio-Cuaternarias. Los resultados geofísicos indican la presencia de zonas de debilidad subsuperficial representadas por una tectónica extensional y zonas meteorizadas las cuales son responsables de la circulación de agua termal y facilitan la recarga desde los cuerpos de aguas superficiales adyacentes. Las estructuras inferidas por los relevamientos de resistividad, tanto sondeos como tomografía eléctrica, presentan contrastes en la respuesta de la resistividad de la roca. Las zonas anómalas en los datos magnéticos están en buen acuerdo con las zonas que son revelados por el mapeo geológico y las manifestaciones en superficie de las zonas de descarga de aguas termales. El acuífero somero del MER central está bajo la influencia de agua termal, la cual incrementa la temperatura y el contenido mineral del agua subterránea.
摘要
为刻画埃塞俄比亚境内一个浅部含水层系统的含水层形态特征以及温泉补给与循环机理,开展了一个包括地质、水文地质和地球物理技术的综合性调查。本文以位于构造活跃的Main Ethiopian Rift (MER)上的Sodere和Gergedi温泉为例。地质上,本文所研究的温泉位于上新世-第四纪火山岩上。地球物理探测结果表明存在有以伸展构造和风化带为代表的地下薄弱地带,是热水循环的原因,并促进了附近地表水体的补给。根据电阻率测量结果(包括测深与电子成像)推断的构造,在岩性电阻率信号上形成对照。基于磁场数据确定的异常区与基于地质填图和排泄区地表热显示所圈定的范围一致。MER中央的浅部含水层受热水影响,提高了地下水温度和矿物质含量。
Riassunto
Al fine di definire le dinamiche di ricarica e di circolazione di sorgenti termali profonde e di delimitare la geometria dell’acquifero superficiale alimentante è stata realizzata un’indagine integrata idrogeologica e geofisica. Le sorgenti Sodere e Gergedi, ubicate all’interno del Main Ethiopian Rift (MER) (Etiopia centrale), sono state selezionate come rappresentative. Nell’area in studio sono presenti rocce vulcaniche riferibili al Plio-Quaternario. Le interpretazioni dei dati geofisici indicano la presenza nel sottosuolo di zone fratturate legate a tettonica estensionale e alterazione, che sono responsabili della circolazione dei fluidi termali e che facilitano la ricarica dai limitrofi corpi idrici superficiali. Le strutture dedotte dalle indagini di tomografia elettrica ed acustica mostrano un contrasto di resistività nelle rocce. Le zone ad anomalia magnetica sono in accordo con quelle evidenziate dalla geologia di terreno e dalle manifestazioni superficiali delle emergenze delle acque termali. L’acquifero superficiale del MER centrale è influenzato dalle acque termali profonde, che fanno aumentare la temperatura e la mineralizzazione delle acque sotterranee.
Resumo
Foi desenvolvido um programa integrado de pesquisa que envolveu técnicas geológicas, hidrogeológicas e geofísicas, para caraterizar a geometria do aquífero e a recarga e a dinâmica da circulação de nascentes termais dentro de um sistema aquífero superficial na Etiópia. As nascentes selecionadas para o estudo de caso foram as de Sodere e Gergedi, situadas dentro do Rift Principal Etíope (Main Ethiopian Rift – MER), que se encontra tectonicamente ativo. Geologicamente, as nascentes estudadas situam-se em rochas vulcânicas de idade Plio-Quaternária. Os resultados geofísicos indicam a presença de zonas de fraqueza na subsuperfície, representadas por tectónica extensional, e zonas de meteorização, as quais são responsáveis pela circulação de águas termais e facilitam a recarga a partir de massas de água superficiais adjacentes. As estruturas inferidas pelos ensaios de resistividade, tanto em sondagem como em tomografia elétrica, apresentam contrastes na resposta da resistividade da rocha. As zonas anómalas nos dados magnéticos estão de acordo com as zonas delimitadas por mapeamento geológico e com as zonas de manifestação superficial da descarga de águas termais. O aquífero superficial do MER encontra-se sob influência de águas termais, aumentando a temperatura e o conteúdo mineral da água subterrânea.
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References
Abebe B, Boccaletti M, Mazzuoli M, Bonini M, Tortorici L, Trua T (1998) Geological map of the Lake Ziway-Asela region (Main Ethiopian Rift). scale 1:50,000, Cons. Naz. delle Ric., ARCA, Florence
Abebe B, Acocella V, Korme T, Ayalew D (2007) Quaternary faulting and volcanism in the Main Ethiopian Rift. J Afr Earth Sci 48:115–124
Abiye TA (2010) Groundwater dynamics in the East African Rift system. In: Xu Y, Braune E (eds) Sustainable groundwater resources in Africa. Taylor and Francis, London, pp 93–106
Abiye TA, Haile T (2008) Geophysical exploration of the Boku geothermal area, Central Ethiopian Rift. Geothermics 37(6):586–596
Acocella V, Korme T, Salvini F, Funiciello R (2002) Elliptic calderas in the Ethiopian Rift: control of pre-existing structures. J Volcanol Geoth Res 119:189–203
Alemayehu T (2000) Water pollution by natural inorganic chemicals in the central part of the Main Ethiopian Rift. Ethiop J Sci 23(2):197–214
Alemayehu T (2003) Controls on the occurrence of cold and thermal springs in central Ethiopia. Afr Geosci Rev l9(4):245–251
Alemayehu T, Vernier A (1997a) Conceptual model for Boku Hydrothermal area, (Nazareth) Main Ethiopian Rift Valley. Ethiop J Sci 20(2):283–291
Ayele T (2001) Geophysical studies in the Aluto Geothermal Area. MSc Thesis. Addis Ababa University, Ethiopia, pp 110
Ayele A, Teklemariam M, Kebede S (2002) Geothermal resources exploration in the Abaya and Tulu Moye-Gedemsa geothermal prospects, Main Ethiopian Rift. Ethiopian Institute of Geological Survey, Addis Ababa, Ethiopia
Bendick R, McClusky S, Bilham R, Asfaw L, Klemperer S (2005) Distributed Nubia–Somalia relative motion and dike intrusion in the Main Ethiopian Rift. Geophys J Int 165(1):303–310
Boccaletti M, Mazzuoli R, Bonini M, Trua T, Abebe B (1999) Plio-Quaternary volcano-tectonic activity in the northern sector of the Main Ethiopian Rift: relationships with oblique rifting. J Afr Earth Sci 29(4):679–698
Chernet T, GebreEgziabher Z (1983) Geothermal geology of the Dofan and Fantale area (Northern Ethiopian Rift). Geothermal Exploration Project, Ethiopian Institute of Geological Survey, Addis Ababa, Ethiopia
Damte A, Bocaletti M, Getaneh A, Mazzouli R, Luigi T (1992) Geological Map of Nazeret-Dera Region. 1: 50000 scale. Florence, Italy
Eyasu S (2008) Integrated Geophysical Investigations at Sodere Thermal Springs, Main Ethiopian Rift, MSc Thesis, Addis Ababa University, Ethiopia, 96 pp
Furi W, Razack M, Haile T, Abiye TA, Legesse D (2011a) The hydrogeology of Adama-Wonji basin and assessment of groundwater level changes in Wonji wetland, Main Ethiopian Rift: results from 2D tomography and electrical sounding methods. J Environ Earth Sci 62:1323–1335
Furi W, Razack M, Abiye TA, Ayenew T, Legesse D (2011b) Fluoride enrichment mechanism and geospatial distribution in the volcanic aquifers of the Middle Awash basin, Northern Main Ethiopian Rift. J Afr Earth Sci 60:315–327
Gianelli G, Teklemariam M (1993) Water–rock interaction processes in the Aluto Langano Geothermal Field (Ethiopia). J Volcanol Geotherm Res 56:429–445
Gizaw B (1993) Aluto-langano geothermal field, Ethiopian Rift valley: physical characteristics and the effects of gas on well performance. Geothermics 22(2):101–116
Gizaw B (1996) The origin of high bicarbonate and fluoride concentrations in the waters of the Main Ethiopian Rift Valley, East African Rift System. J Afr Earth Sci 22(4):391–402
Haile T, Alemayehu T, Fisseha S (2002) Geophysical Investigations of the Boku Thermal Springs, Nazareth. Ethiop J Sci 25(2):253–262
Kazmin V, Berhe S (1978) Geology and development of the Nazareth area. Ethiopian Institute of Geological Survey, Addis Ababa, Ethiopia
Korme T, Acocella V, Abebe B (2004) The role of pre-existing structures in the origin, propagation and architecture of faults in the Main Ethiopian Rift. Gondwana Res 7(2):467–479
Mohr PA (1967) The Ethiopian Rift system. Bull Geophys Obs Addis Ababa 5:33–62
Mohr PA, Zanettin B (1988) The Ethiopian flood basalt province. In: Macdougall JD (ed) Continental Flood Basalts. Kluwer, Dordrecht, The Netherlands, pp 63–110
NOAA (2010) International Geomagnetic Reference Field (IGRF) model parameters vol. 3, http://www.ngdc.noaa.gov/geomag/models.shtml. Cited 02 Dec. 2010
Oberlin A, Couty R (1970) Conditions of kaolinite formation during alteration of some silicates by water at 200°C. J Clay Clay Miner 18:347–356
Peccerillo A, Barberio MR, Yirgu G, Ayalew D, Barbieri M, Wu TW (2003) Relationships between mafic and peralkaline silicic magmatism in Continental Rift settings: a petrological, geochemical and isotopic study of the Gedemsa Volcano, Central Ethiopian Rift. J Petrol 44(11):2003–2032
Tanya F, Bryce J, Karson J, Iotti A (2004) East African Rift System (EARS) plume structure: insights from Quaternary mafic lavas of Turkana, Kenya. J Petrol 45(5):1069–1088
Teklemariam M, Battaglia S, Gianelli G, Ruggieri G (1996) Hydrothermal alteration in the Aluto-Langano geothermal field, Ethiopia. Geothermics 25(6):679–702
Thrall R (1973) Gedemsa Caldera, Ethiopia. Center for Astrophysics, Dartmouth College, Hanover, NH, pp 71–80, Reprint Series 280
UNDP (1973) Investigation of geothermal resources of power development: geology, geochemistry and hydrogeology of hot springs of the east African Rift System within Ethiopia. Ethiopian Institute of Geological Survey, Addis Ababa, Ethiopia
WoldeGabriel G, Walter RC, Aroson JL, Hart WK (1992) Geochronology and distribution of silicic volcanic rocks of Plio-Pleistocene age from the central sector of the Main Ethiopian Rift. Quat Int 13(14):69–76
Acknowledgements
One of the authors, T. Haile, wants to thank the Office of Vice President for Graduate Studies and Research, Addis Ababa University, for granting him the funds for carrying out the geophysical work. The write up of the initial manuscript was done while he was visiting the Grant Institute of Geosciences, University of Edinburgh and he wants to thank his host, C. Whaler, for providing him with the necessary facilities and support.
T. Abiye thanks the NRF (National Research Foundation) of South Africa for the financial support to undertake part of the research.
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Haile, T., Abiye, T.A. The interference of a deep thermal system with a shallow aquifer: the case of Sodere and Gergedi thermal springs, Main Ethiopian Rift, Ethiopia. Hydrogeol J 20, 561–574 (2012). https://doi.org/10.1007/s10040-012-0832-8
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DOI: https://doi.org/10.1007/s10040-012-0832-8